Project Summary Fragile X syndrome (FXS) is characterized with hyperactivity, intellectual disability, sensory dysfunction, and difficulties in social communication. This disorder is caused by the loss of the Fmr1 gene product, the fragile X mental retardation protein (FMRP). The aim of this project is to develop a loss-of-function model of Fmr1 in the Mongolian gerbil (Meriones unguiculatus). A key rationale for developing this model lies in the excellent sensitivity of this gerbil species to low frequency sounds: These animals display an audiogram comparable to humans. Given the essential role of low frequency hearing in human binaural interaction, acoustic scene analysis, and vocal communication, studying how FMRP loss impairs neuronal processing of low frequency sounds is expected to provide an important and likely necessary avenue for understanding FXS pathology. Unfortunately, current rodent models of FXS were developed in high frequency listeners (mice and rats). Recent advancement in CRISPR-Cas9 gene-editing technologies and our completion of the de novo sequencing of the gerbil genome have established the technical feasibility of producing targeted gene disruption in gerbils. In collaboration with the University of Washington (Curnow), we will accomplish our aim by generating a CRISPR-mediated knockout (KO) of Fmr1 in gerbil embryos, transferring the embryos for pregnancy and live born pups, and identifying founder animals and establishing an Fmr1 KO gerbil colony. We will then perform a battery of characterizations that will utilize behavioral and functional assays of characteristic FXS phenotypes, including hyperactivity and acoustic hypersensitivity. In addition, cellular abnormalities common to human and rodent FXS brains will be assessed anatomically in Fmr1 KO gerbils. We will also initiate studies that will examine the hypothesis that low frequency hearing is compromised in Fmr1 KO gerbils, if time permits. The successful completion of this project will fill a critical need for animal models that more closely recapitulate the hearing and communication deficits observed in FXS humans. A Fmr1 KO gerbil strain has the potential to provide the essential link between FMRP neurobiology and auditory perception deficits in FXS.